3.2 Basic principles of supercritical fluid chromatography and  (Page 6/6)

Extraction modes

There are two modes in terms of collecting and detecting the components:

• Off-line extraction.
• On-line extraction.

Off-line extraction is done by taking the mobile phase out with the extracted components and directing them towards the collection chamber. At this point, supercritical fluid phase is evaporated and released to atmosphere and the components are captured in a solution or a convenient adsorption surface. Then the extracted fragments are processed and prepared for a separation method. This extra manipulation step between extractor and chromatography instrument can cause errors. The on-line method is more sensitive because it directly transfers all extracted materials to a separation unit, mostly a chromatography instrument, without taking them out of the mobile phase. In this extraction/detection type, there is no extra sample preparation after extraction for separation process. This minimizes the errors coming from manipulation steps. Additionally, sample loss does not occur and sensitivity increases.

Applications of sfe

SFE can be applied to a broad range of materials such as polymers, oils and lipids, carbonhydrates, pesticides, organic pollutants, volatile toxins, polyaromatic hydrocarbons, biomolecules, foods, flavors, pharmaceutical metabolites, explosives, and organometallics, etc. Common industrial applications include the pharmaceutical and biochemical industry, the polymer industry, industrial synthesis and extraction, natural product chemistry, and the food industry.

Examples of materials analyzed in environmental applications: oils and fats, pesticides, alkanes, organic pollutants, volatile toxins, herbicides, nicotin, phenanthrene, fatty acids, aromatic surfactants in samples from clay to petroleum waste, from soil to river sediments. In food analyses: caffeine, peroxides, oils, acids, cholesterol, etc. are extracted from samples such as coffee, olive oil, lemon, cereals, wheat, potatoes and dog feed. Through industrial applications, the extracted materials vary from additives to different oligomers, and from petroleum fractions to stabilizers. Samples analyzed are plastics, PVC, paper, wood etc. Drug metabolites, enzymes, steroids are extracted from plasma, urine, serum or animal tissues in biochemical applications.

Summary

Supercritical fluid chromatography and supercritical fluid extraction are techniques that take advantage of the unique properties of supercritical fluids. As such, they provide advantages over other related methods in both chromatography and extraction. Sometimes they are used as alternative analytical techniques, while other times they are used as complementary partners for binary systems. Both SFC and SFE demonstrate their versatility through the wide array of applications in many distinct domains in an advantageous way.

Bibliography

• M. Caude and D. Thiebaut, Practical Supercritical Fluid Chromatography and Extraction , Harwood Academic Publishers, Switzerland (1999).
• M. D. Luque de Castro, M. Valcarcel, and M. T. Tena, Analytical Supercritical Fluid Extraction , Springer-Verlag, Berlin (1994).
• D. A. Skoog and J. J. Leary, Principles of Instrumental Analysis , Saunders College Publishing, Philadelphia (1992).
• L. T. Taylor, Supercritical Fluid Extraction , Wiley-Interscience Publication, New York, (1996).